Piezoelectric ceramic materials



1969 KAZUNOBU KURIHARA ETAL 3. 7 3

PIEZOELECTRIC CERAMIC MATERIALS 2 Sheets-Sheet 2 Filed Nov. 15, 1967FIG. 3

z w w v. m w w o 4 Awr firfl mczazoo Hoo ur-omEotom m a 1'0 Proportionof B01103 (mol c i L T IXYENTOR.

BY Mb United States Patent Office 3,472,779 PIEZOELECTRIC CERAMICMATERIALS Kazunobu Kurihara, Noboru Ichinose, Yoshikazu Tanno,

and Katsunori Yokoyama, Yokohama-shi, Japan, assignors to Tokyo ShibauraElectric Co., Ltd., Kawasakishi, Japan, a corporation of Japan FiledNov. 15, 1967, Ser. No. 683,254 Claims priority, application Japan, Nov.22, 1966,

1/ 76,374 Int. Cl. C04b 35/48, 35/46 US. Cl. 252-623 2 Claims ABSTRACTOF THE DISCLOSURE This invention relates to piezoelectric materialshaving piezoefiect and more particularly to ferroelectric ceramicmaterial of the lead-zirconium-titanium series.

One of the known piezoelectric materials consists of a solid solution oflead titanate and lead zirconate which i represented by the followinggeneral formula:

This material, however, has a poor electromechanical couplingcoeflicient, for example, less than 40%, even when the material consistsof a composition shown by said general formula wherein x is in a rangeof from 0.45 to 0.50 which exhibits the most favourable piezoelectriccharacteristic due to a morphotropic phase transition.

Materials having compositions represented by the following generalFormulae 2 and 3 which are modifications of said Formula 1,

and materials having compositions wherein a portion of Pb of thecompositions represented by said Formulae 1 and 3 are replaced by lessthan 30 mol percent of Sr, Ba or Ca are also known in the art. Althoughthese materials have improved electromechanical coupling'coefficientover the material of the composition represented by Formula 1 whenpowders of constituents of these compositions are sintered by powdermetallurgy technique to obtain ceramic articles, high sinteringtemperatures are required owing to their insuflicient sinterability andyet sintered articles obtained have relatively large porosity.

It has been proposed to incorporate oxides of trivalent or pentavalentmetals such as Sb O and Nb O to the composition shown by Formula 1.These materials accompany evaporation loss of the PhD component whichhas the lowest boiling point during its sintering, and changes in thecomposition will cause the desired piezoelectric characteristic to vary.

This invention contemplates providing a novel piezoelectric ceramicmaterial of lead zirconate-lead titanate series consisting of 40 to 50mol percent of PbTiO 0.5

to 6 mol percent of Ba(MeNb) O (where Me represents an element selectedfrom the group consisting of In, Y, La, Na, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb and Lu) and the remainder of PbZrO A portion of PbTiO may besubstituted by less than 10 mol percent, based on the total quantity ofthe material of BaTiO Patented Oct. 14, 1969 When sintered underordinary temperature conditions, the piezoelectric material shows highelectromechanical coupling coefficients of more than 40% and high bulkdensities of more than 7.5 g./cm.

This invention can be more fully understood from the following detaileddescription taken in connection with the accompanying drawings, inwhich:

FIG. 1 shows a graph representing the relation between electromechanicalcoupling coefiicient and varying ratios of PbTiO and PbZrO of thepiezoelectric material according to this invention;

FIG. 2 is a graph showing the relation between electromechanicalcoupling coefficient and Ba(YN-b) O for three types of the materials;and

FIG. 3 is a graph to show the electromechanical coupling coefiicient oftwo materials, a portion of PbTiO thereof has been replaced by varyingamount of BaTiO The proportion of each component of the novelpiezoelectric ceramic material is selected to give sufiicient physicalproperties, especially high electromechanical coupling coefiicient tothe material.

When the material contains 40 to 50 mol percent of PbTiO component ithas electromechanical coupling coeflicient Kr of more than 40% suitablefor many practical applications. For example, FIG. 1 shows variation inKr for various proportions of PbTiO and 'PbZrO in a compositioncontaining 4 mol percent of'Ba(YNb O In this composition, proportions ofPbTiO of 45.5% and PbZrO of 50.5% gives highest Kr whereas PbTiO of lessthan 40% and in excess of 50% lowers Kr to less than 40%.

In order that the piezoelectric material may have desirable Kr of morethan 40%, the proportion of Ba(MeNb) O should be in a range of from 0.5to 6 mol percent. FIG. 2 shows the relation between Ba(MeNb) O and Kr.In this figure curve A shows the result of measurement made of amaterial consisting of 45.0 mol percent of PbTiO various amounts ofBa(YNb) O and the remainder of PbZrO curve B shows the result of amaterial of the similar composition except that the proportion of PbTiOis 48.0 mol percent and curve C shows that of a material containing 41.0mol percent of PbTiO As can be noted from these curves, materialscontaining from 0.5 to 6 mol percent of Ba(MeNb) O exhibit a value of Krexceeding 40%.

In materials represented by the general formula Ba(MeNb) O Me representsan element selected from the group consisting of In, Y, La, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Each .of these elements belongs toGroup III of the Periodic Table and when incorporated into the materialaccording to said general formula greatly improves Kr.

A portion of PbTiO may be replaced by BaTiO of the amount not exceeding10 mol percent of the total compositions of the material. Materialscontaining BaTiO within this range provide excellent Kr of more than 40%together with improved values of dielectric constant. It was found thatalthough increase in the proportion of BaTiO contributes to proportionalimprovements of dielectric constant, proportions in excess of 10 molpercent decrease Kr to less than 40%. Curves D and E of FIG. 3 show therelation between the proportion of BaTiO and Kr of two materials of thisinvention when a portion of PbTiO- is substituted by BaTiO of varyingproportions. Curve D shows the result of measurement made on a materialconsisting of 48 mol percent of PbTiO 4 mol percent of Ba(YNb) O and theremainder of PbZrO' whereas curve B shows that of a material consistingof 43 mol percent of PbTiO 4 mol percent of Ba(YNb) O and the remainderof PbZrO in both materials a portion of PbTiO being substituted byvarying proportions of BaTiO While there is a slight 3 dilferencedependent upon variations in composition where the proportion of BaTiOexceeds 10 mol percent, Kr of the material is lowered to less than 40%.

The piezoelectric materials can be manufactured by the powder metallurgytechnique like conventional materials of the same type. According to themost common method, a granular material of the average particle size ofabout 0.5 to 1 micron is used as the raw material which is moulded intothe desired configuration, and then sintered at a temperature rangingfrom 1200 to 1300 C., for example. In order to facilitate moulding, theraw material may contain a solution of a resinous binder such as anaqueous solution of polyvinyl alcohol. This resinous binder undergoesdecomposition and vapourizes off from the raw material when heated tothe sintering temperature.

The raw material may be a mixture which consists of compounds includingelements in such proportions as to produce the above described oxideupon sintering. Generally, the compound may be oxides, hydroxides,carbonates or oxalates. Preferably, after mixing, these compounds areburned prior to sintering at a. temperature lianging from 600 to 900 C.and then pulverised.

It is advantageous to sinter the raw material in a sealed furnace inorder to avoid variation of the proportion of components due tovapourization.

When compared with materials of conventional composition prepared frompowdered raw materials having the same particle size and sintered at thesame temperature, the sintered materials of this invention have a largerbulk density. It is presumed that this is caused by the fact thatpresence of Ba(MeNb) O having the perovskite structure contributes tothe improvement of the sinterability of the raw material. For example,Ba(YNb) O has the perovskite structure wherein the lattice constant a isequal to 8.43 angstroms. When a raw material which has an averageparticle size of 0.5 to 1 micron is sintered at a temperature rangingfrom 1250 to 1300 C., the sintered material has a bulk density of 7.5g./cm. or higher. This should be compared with materials of conventionalcompositions having bulk densities of less than 7.0 g./cm. even whensintered at temperatures exceeding 1300 C. Such an excellentsinterability will permit use of lower sintering temperatures wherebyloss of most volatile PbO can be avoided.

The piezoelectric materials of this invention have another advantagethat the variation in piezoelectric characteristic with the variation ofthe proportion of the components is very small. This alleviatesconditions for mixing the raw material and for sintering thus assuringmaterials having uniform piezoelectric characteristic. Generally, fromthe result of experiments, variations in the proportion of therespective components of less than -0.5% does not materially affect thepiezoelectric characteristic of the material. Further, with respect tothe piezoelectric characteristic the novel materials are stable againsttemperature variation as well as elapse of time after pulverization,such a stability contributes to improve reliability of the material.

The following specific examples are given by way of illustration and arenot to be construed as limiting in any way the specific scope and spiritof the invention. In the examples, bulk density is given by a value ot26 C. whereas dielectric constant and dielectric loss are given byvalues measured by an alternating current having a frequency of 1kc./sec.

EXAMPLE 1 200.9 g. of PbO, 14.83 g. of BaO, 36.8 g. of TiO;, 61.5 g. ofZrO 2.26 g. of Y O and 2.62 g. of Nb O were mixed and pulverised in aball mill, burned at a temperature of 700 C. for 90 minutes and againpulverised in a ball mill. The average particle size of this powder wasabout 1 micron. The powder was then mixed with a suitable quantity of anaqueous solution of polyvinyl alcohol and moulded into a circular dischaving a diameter of 13 mm. and a thickness of 1 mm., by pressing undera pressure of 1000 kg./cm. The disc was sintered in a sealed furnace byheating it to a temperature of 1280 C. for one hour. The disc obtainedhad a bulk density of 7.58 g.//cm. a Curie temperature T of 300 C., anda composition consisting of 40.0 mol percent of PbTiO 6.0 mol percent ofBaTiO 4.0 mol percent of Ba(YNb) O and the remainder of PbZrO A pair ofelectrodes were attached to this to measure its dielectric properties,and obtained as dielectric constant (e) of 1510 and dielectric loss (tan6) of 1.3%.

This disc was then polarised at C. by applying a DC voltage of 4 kv.across it for one hour. After standing it in atmospheric air for oneweek, its piezoelectric characteristics were measured and obtained thefollowing result:

Electromechanical coupling coeflicient Kr: 62.3% (27 0). Mechanicalquality factor: 120.

EXAMPLE 2 Similar to Example 1, 198.7 g. of PbO, 16.9 g. of BaO, 39.0 g.of TiO 60.5 g. of ZrO 1.38 g. of In O and 1.33 g. of Nb O were burnedand pulverised. The granular raw material obtained was moulded into adisc having a diameter of 13 mm. and a thickness of 1 mm. by pressingunder a pressure of 1000 kg./cm. This disc was sintered by heating to atemperature of 1260 C. for 90 minutes. The sintered disc had acomposition consisting of 40.0 mol percent of PbTiO 9.0 mol percent ofBaTiO 2.0 mol percent of Ba(InNb) O and the balance of PbZrO Its bulkdensity was 7.60 g./cm. and its Curie temperature T was 295 C.

Electrical characteristics were as follows:

tan 6: 1.5%

10 ohm-cm. Kr=43.1% Qm=180 EXAMPLE 3 Similar to Example 1, 217.7 g. ofPbO, 1.27 g. of BaO, 36.2 g. of TiO 64.1 g. of ZrO 0.66 g. of La O and0.57 g. of Nb O were burned, moulded and then sintered at a temperatureof 1240 C. for two hours. A resulted circular disc shaped piezoelectricmaterial had a bulk density D of 7.65 g./crn. and a Curie temperature of338 C.

EXAMPLE 4 213.9 g. of PbO, 6.14 g. of BaO, 36.1 g. of TiO 62.9 g. of ZrO2.75 g. of Nb O and 3.37 g. of Nd O were pulverised and mixed in a ballmill, burned at a temperature of about 800 C., moulded into a circulardisc having a diameter of 13 mm. and a thickness of 1 mm. by pressingunder a pressure of 1000 kg./cm. and then sintered by heating to atemperature of 1270 C. for one hour. The composition of this disc wascomprised by 45.0 mol percent of PbTiO 4.0 mol percent of Ba(NdNb) O andthe remainder of PbZrO EXAMPLE 5 As in Example 4, Nd O was substitutedby 3.41 g. of Sm O and the material is sintered to obtain a circulardisc having a composition consisting of 45.0 mol percent of PbTiO 4.0mol percent of Ba(SmNb) O and the remainder of PbZrO 5 EXAMPLE 6 As inExample 4, 3.50 g. of Gd O was substituted for Nd O and a similarceramic containing 4.0 mol percent of Ba(GdNb) O was obtained.

EXAMPLE 7 As in Example 4, in lieu of Nd O 3.52 g. of Tb O was used anda similar ceramic containing 4.0 mol percent of Ba(TbNb) O was obtained.

EXAMPLE 8 As in Example 4, Nd O was replaced by 3.56 g. of Dy O toobtain a similar piezoelectric material containing 4.0 mol percent ofBa(DyNb) was obtained.

EXAMPLE 9 As in Example 4, 3.63 g. of H0 0 was substituted for Nd O anda similar ceramic containing 4.0 mol percent of Ba(HoNb) O was obtained.

EXAMPLE 10 As in Example 4, Nd O component was substituted by 3.63 g. ofTm O to obtain a ceramic disc containing 4.0 mol percent of Ba(TmNb) OEXAMPLE 11 As in Example 4, Nd O was replaced by 3.71 g. of Yb O toprepare a similar ceramic containing 4.0 mol percent of Ba(YbNb) OEXAMPLE 12 As in Example 4, Nd O was substituted by 3.42 g. of Eu O toobtain a piezoelectric disc containing of 4.0 mol percent of Ba(EuNb) OPhysical characteristics of various piezoelectric materials preparedaccording to Examples 4 through 11 were as follows.

D (g. [cm e Kr(percent) Qm EXAMPLE 13 As in Example 1, a raw mixtureconsisting of 202.2 g. of PbO, 10.66 g. of BaO, 37.3 g. of TiO 67.3 g.of ZrO 3.28 g. of Nb O and 4.76 g. of Er O was used, burned, mouldedinto a circular disc having a diameter of 13 mm. and a thickness of 1mm. and then sintered at a temperature of 1290 C. The sintered disc hada composition consisting of 38.5 mol percent of P-bTiO 2.5 mol percentof BaTiO 5.0 mol percent of Ba(ErNb) O and the remainder of PbZrO andhad the following physical characteristics D=7.79 g./cm.

tan &=3.1%

p: 10 ohm-cm.

EXAMPLE 14 A mixture consisting of 218.6 g. of PbO, 3.03 g. of BaO, 35.2g. of TiO 67.3 g. of ZrO 0.72 g. of Nb O and 0.88 g. of Gd203 wasmoulded into a circular disc of 13 mm. diameter and 1 mm. thick afterthe mixture was burned at temperature of about 800 C., and then sinteredat 1260 C. for minutes. The disc shaped piezoelectric ceramic had acomposition consisting of 43.5 mol percent of PbTiO 1.0 mol percent ofBaTiO 1.0 mol percent of Ba(GdNb) O and the rest of PbZrO and had thefollowing characteristics:

where Me is an element selected from the group consisting of In, Y, La,Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and the remainder ofPbZrO and such materials wherein a portion of said PbTiO is replaced byBaTiO in a proportion not exceeding 10 mol percent based on the totalquantity of said materials.

2. The piezoelectric ceramic materials according to claim 1 wherein aportion of said PbTiO is replaced by BaTiO in a proportion not exceeding10 mol percent based on the total quantity of said materials.

References Cited UNITED STATES PATENTS 3,068,177 12/1962 Sugden 252-6293,268,453 8/1966 Ouchi et al. 252-629 3,268,783 8/1966 Saburi 10639 XTOBIAS E. LEVOW, Primary Examiner J. COOPER, Assistant Examiner US. Cl.X.R. 10639

